Re: chipidea: udc: kernel panic in isr_setup_status_phase

[Peter Chen <hzpeterchen@gmail.com>]

On Tue, Aug 30, 2016 at 07:20:45PM +0200, Clemens Gruber wrote:
> On Mon, Aug 29, 2016 at 06:24:03PM +0800, Peter Chen wrote:
> > Would you please measure the voltage of vbus within 1s at below two
> > conditions:
> > 
> > - Just connect cable
> > - Just disconnect cable
> 
> We found out that there was a problem with our hardware design!
> 
> But first, here is the VBUS measurement during cable plug-in.
> https://s17.postimg.org/8ba3rgl6n/linux_kernel_panic_usb_otg_vbus_is_yellow.jpg
> (The yellow signal is USB_OTG_VBUS, please ignore the red one)
> The kernel panic occurs where the slip of paper with the arrow is.
> The signal looks normal to me, I don't think VBUS was the problem.
> 

Do you have other 5V to USB_H1_VBUS? USB PHY needs 5V input voltage
as the source for USB LDO (3.0v), either from OTG or Host 1. I suspect
the lower vbus voltage causes the USB LDO voltage less than 3.0v, then
cause the unstable for USB PHY. If possible, you can connect MAIN 5V
(if it exists) directly to USB_H1_VBUS to see if this problem is fixed.

> The other theory was a GND problem..
> After thorough investigation, we discovered that we connected all
> SHIELD pins of the USB micro OTG connector to the protective-earth
> ground (GND_PE) with a 1 MOhm resistor and a 1 nF cap in parallel.
> We changed that to connect the SHIELD pins to the same internal GND
> as the USB signals have and also replaced the 1 MOhm resistor with a
> 100 Ohm  resistor as seen in the MCIMX6Q-SDB schematics.
> Since that change, the error did not appear again! :)

Great. Can you see the sudden lower for vbus again? If it still exists, it may
be GND issue.

> 
> The only signals I never checked are the differential high speed signals
> (USB_OTG_DN and USB_OTG_DP) because I don't have the necessary equipment
> like active differential probes for very high frequency measurements, ..
> Maybe with the connection of the shield to PE, the cable acted as an
> antenna and interfered with the high speed signals?


> (Although they are differential, so the same noise to both should not
> be a problem? It is still a mystery to me, what was really causing it)
> 

The poor signal may cause the controller has unexpected behavior.

> 
> What do you think about still fixing that kernel panic in case something
> similar happens again for other users?
> If such a situation occurs, should we only avoid the NULL pointer
> dereference or print out an error message and stop the gadget driver?
> 

Avoid NULL pointer deference is necessary. Patch is welcome :)

-- 

Best Regards,
Peter Chen